The present invention relates to ultra-wide band optical digital coherent detection.
Submarine optical networks form the backbone of global communication networks. Submarine optical networks usually consist of main trunks that connect the trunk terminals, which are point-to-point cable links with in-line optical amplifiers to boost the signal power, and branch path that connect to other branch terminals. A branching unit (BU) is a network element that splits the signal between the main trunk and the branch path and vice versa. This allows the signals from different paths to share the same fiber, instead of installing dedicate fiber pairs for each link. The signal splitting and combining function of the BU is usually performed optically, therefore the BU has the similar function as the optical add/drop multiplexer (OADM) in the terrestrial WDM networks. FIG. 1 shows the schematic of existing submarine communication system that consists of two trunk terminals, one branch terminal and one BU that links the main trunk with the branch path. Bidirectional fiber transmission is illustrated. Note that there are there are two pairs of fiber between the BU and the branch terminal. One pair is used to connect Trunk Terminal 1 to the branching terminal, while the second pair is used between Trunk Terminal 2 and the branch terminal. This allows the reuse of the same wavelengths in the TT1-BT path and the TT2-BT path.